1. Technical Field
The present invention relates to an illuminator, an image display apparatus, and a polarization conversion/diffusion member.
2. Related Art
In recent years, there is widely known a projector in which an illuminator illuminates a light modulator and a projection optical system, such as a projection lens, enlarges and projects image light outputted from the light modulator on a screen.
A metal halide lamp, a halogen lamp, and other lamps have been used as the illuminator in the projector. In recent years, however, it has been proposed to use a semiconductor laser (LD) to reduce the sizes of the illuminator and the projector. Advantages of a laser light source include not only compactness but also excellent color reproducibility, image display with high brightness and contrast, and quick start.
However, since laser light is coherent, enlarged and projected image light produces a speckle pattern having bright and dark dots randomly distributed. Such a speckle pattern occurs when interference occurs between light beams that exit from various locations in a projection optical system and have randomly different phases. An image having such a speckle pattern disadvantageously gives a viewer a sense of glaring flicker.
To solve the problem, image display apparatus have been proposed in which light emitted from a light source is diffused in a diffuser plate to reduce speckle noise (see JP-A-6-208089, JP-A-2005-84117, and JP-A-2006-53495, for example).
In the display apparatus described in JP-A-6-208089, light emitted from a laser light source is diffused in a diffuser element, and the diffused light is focused by a lens onto a spatial light modulator. The light converted into an image by the spatial light modulator is then displayed on a viewing screen.
In the projection-type image display apparatus described in JP-A-2005-84117, light emitted from a one-dimensional display device is scanned by a galvanometric scanner, and the scanned light passes through an oscillating diffuser. The light is diffused in the diffuser, outputted therefrom, and enlarged and projected on a screen through a projection lens.
In the image display system described in JP-A-2006-53495, a first optical system focuses light emitted from a light source to form an intermediate image on an optical diffusion angle converter, and the optical diffusion angle converter enlarges the incidence angle of the light incident thereon and outputs the light therefrom with the enlarged exit angle. Oscillating the optical diffusion angle converter allows temporal change in speckle pattern to be integrated in human eyes and hence speckle noise to be reduced.
In the technologies described in JP-A-6-208089 and JP-A-2005-84117, however, light emitted from the light source is diffused in the diffuser plate to reduce speckle noise, but it is difficult to reduce speckle noise to a level at which human eyes cannot perceive any noise by relying only on the diffuser plate.
In the technology described in JP-A-2006-53495, optimizing the relationship between the scattering angle at the optical diffusion angle converter and the introduction angle at a projection lens allows a large number of scatter patterns to be projected on the screen, whereby a bright image with reduced speckle noise can be projected. In this configuration, again, it is difficult to reduce speckle noise to a level at which human eyes cannot perceive any noise.